How would I attach text to a tracked point on video clip
Let's say you've successfully tracked an object in your scene:



Go to the Solve Tab and in the Geometry section and click on Link Empty To Track.



That will create an Empty that, if seen from the camera, moves within the frame like the tracked object.



At this point you might want to add your image as background for reference and make it visible for the camera axis.

Add a text object in the 3d View (ShiftA > Text ) and select the Align to View option:



Edit your text, set the orientation to view and place it where you need it.



Select your text object, then select the Empty by holding Shift and simply parent it to the Empty (CtrlP).

The text will now move like the tracked object.



To render both images create a node tree like this:

 

If the text element is an image and not a 3D object

You can overlay the background video with the foreground element using the compositor:



The text (with a transparent background) is placed and scaled with a transform node.

The result of that is then passed to a translate node that uses the information from the tracker (select the video used and the object, usually "camera" and the tracker you want to use to control the movement)



Then use an Alpha over to overlay the image on top of the video background.

Tracked image in the  Movie Clip editor:



Result: